feat(yami): add dataDir option for storing stack state on separate disk

- Bind-mounts /var/lib/{gitea,postgresql} under configurable dataDir
- gitea-runner intentionally excluded: its DynamicUser + StateDirectory
  conflicts with pre-existing mount points ("File exists")
- Runner token moved to /var/lib/gitea-runner-secret/ to avoid the same
  symlink/StateDirectory conflict inside /var/lib/gitea-runner
- Enable the stack on this host with dataDir = /mnt/ssd_110/yami

configuration.nix

@@ -7,7 +7,7 @@
     ./desktop.nix
     ./nvidia.nix
     ./shell.nix
-    # ./yami-dev-stack.nix  # uncomment to enable Yami dev stack, then set services.yami-dev-stack below
+    ./yami-dev-stack.nix 
   ];
 
   nix = {
@@ -98,5 +98,11 @@
   # Docker is now managed by yami-dev-stack.nix when that module is enabled.
   # services.yami-dev-stack = { enable = true; user = "chexit"; };
 
+  services.yami-dev-stack = {                               
+    enable = true;                                                                                        
+    user   = "chexit";
+    dataDir = "/mnt/ssd_110/yami";
+  };  
+
   system.stateVersion = "25.11";
 }